The plot is basic and predictable which isn't an inherently bad thing except that some of the characters, most notably the "main" Van Helsing, flip flop personalities and values so often it makes me wonder if they're schizophrenic. Often this seems to be done to force one plotline or another along, or to keep a character "alive" for... reasons.
Additionally every single character the main group encounters is universally "evil", either going to betray them or already betraying people or just messed up in some psychopathic way. While these can be interesting things on their own, its just boring when the moment a new group is shown or introduced you immediately know roughly what's going to happen. Top that off with the main characters psychically knowing something is wrong even when there is no reason to suspect anything and it makes for a very dull viewing experience.
Frankly this show could be good if the characters were consistent in their personalities or values, and if the fringe characters were not universally "evil". The show relies solely on action sequences which while good are not enough to carry it.